| Objectives:To explore the association between congenital absence of permanent mandibular incisors and mandibular mental morphology in chinese orthodontic patients.Methods:In our researth a total of 50 teenages were selected as the subjects from the files of orthodontic patients who had first visit at Department of Orthodontics of the Stomatological Hospital of Luzhou Medical College.All subjects are divided into three groups.A total of 35 teenages of 12-14years old with one or two congenitally absent mandibular incisors(group M) were selected and divided into group 2 (15girls with the absence of one incisor) and group 3 (20 girls with the absence of two incisors). In addition,20 other teenages without hypodontia and with little or no mandibular incisor crowding were enrolled as a control (group 1). All subjects are 12-14 years old.they are no extraction,orthodontic treatment,prosthetic histry. Examination missing location, missing quantity,maxillofacial skeletal patterns, Bontln index are analysised.with congenital lower anterior teeth wUsing the lateral cephalogram of each subject,18 item measurements were made for evaluation of mandibular mental morphology and dentalfaical morphology. The cephalometric data thus obtained were statistically analyzed and compared between the groups with SPSS13.0.Results:1.Survey of congenitally absent mandibular incisors conditions:There were 23 female of the total 35 patients and there were 12male. The ratio of female and male was about 2:1. Fifteen patients were with only one incisor loss, with ratio 42.85%; Tweenty patients among them with two incisors congenital loss,with ratio 57.14% 2. The ratio of facial type:. Among the 35 patients there were 37.14% skeletal typeâ… ,57.14% skeletaltypeâ…¡and 5.71% skeletal typeâ…¢; the constitunt ratio of vertical skeletal face type was average vertical skeletal face type 60.00%, greater vertical skeletal face type 34.29%, smaller verticalskeletal type 5.71%.3. the result of Bolton index analysis:Index of Bolton analysis of the patients of congenitally absent mandibular incisors was smaller than the normal ones,especial in anterior teeth ratio.4. Our research suggest that there was no significant differences in cephalometric measurements(skeletal index and dental index) between the patients with one or tow congenital absence of permanent mandibular incisors. The ongenital absence of permanent mandibular incisors group showed smaller L1-MP angle,LI-NB and LI-NB angle and increased SNB,ANB,Y-axis compared to the control group.5. Effect of congenitally missing permanent mandibular incisors on morphometric of the mental:our research sugges that no significant differences in cephalometric measurements of morphometric of the mental was found between the patients with one or tow congenital absence of permanent mandibular incisors. The congenital absence of permanent mandibular incisors group showed smaller chin height,chin thickness,chin back thickness,chin minimum thicknesss,chin angle compared to the control group. Conclusions: 1. Teenages with congenital absence of mandibular incisor are obviously more female than male, Teenages with two congenital absence of mandibular incisor are slightly more than those with one congenital absence of mandibular incisor2.Teenages with congenital absence of mandibularincisor might have more skeletal classâ…¡appearance, least class I appearance;. The constituent ratio of averagevertical skeletal type was most great,and the second wasr vertical skeletal type.3 The congenital loss of permanent mandibular incisors group showed greater retroclination of chin and greater retroclination of mandibular incisors compared to the control group. 4.We can found significant differences in cephalometric measurements of morphometric of the mental between teenages group with congenital absence of mandibular incisor and controle group;morphometric of the mental region should be taken into consideration in planning orthodontic treatment on patients with congenitally missing permanent mandibular incisors.
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